International Application No. PCT/US94/05567 (International Publication No. 94/27137, published Nov. 24, 1994) to the University of Utah Research Foundation discloses an apparatus for multi-analyte homogeneous fluoroimmunoassays. In one embodiment, the application discloses an apparatus which uses a biosensor having a planar waveguide sandwiched, with an associated gasket, between two plates (FIGS. 3A-3C of Internat'l Publ. No. 94/27137). The inner edges of the gaskets serve as walls for a reaction reservoir or well. Fluorescence-emitting tracer molecules are bound to the waveguide surface and are excited by an evanescent field penetrating into the adjacent solution from a light beam propagated within the waveguide, the beam being introduced at, for example, a front end of the waveguide. In the reaction reservoir, a liquid (e.g. serum or blood) is introduced and is allowed to admix with capture molecules associated with the waveguide surface (e.g. by "coating chemistry" as disclosed on pages 32 to 33 of the international application). The emitted fluorescence is then directly collected from the zone of evanescent penetration. In one particular embodiment, the biosensor has transparent walls which define the reservoirs. (E.g., FIGS. 11A-C of Internatl. Publn. No. 94/27137). The application also discloses integrally formed or molded biosensors. E.g., FIGS. 12A, 12B & 13 of Internatl. Publn. No. 94/27137).
Unfortunately, the waveguide portion of integrally formed or molded biosensors may exhibit deformation upon fabrication, or warping during storage or temperature changes. Also, gaskets may not reliably seal or are not always sufficiently inert to reactants, and thus may interfere with the desired analysis.
It would be desirable to have a biosensor having reservoirs with inert walls, the walls being readily detachable from the waveguide so that one waveguide could be readily exchanged for another.